To complete a well, at least one formation zone may be perforated to allow fluid to flow from the formation into the well for production or to flow out of the well during injection into the surrounding formation zone or zones. A perforating gun string may be lowered into the well along a casing lined wellbore until positioned adjacent a desired formation zone. The perforating guns of the gun string may then be fired to create openings through the casing and to extend these perforations into the surrounding formation.
The explosive nature of the perforating operation tends to shatter sand grains of the formation during creation of perforation tunnels. Consequently, a shock damaged region may be created around the perforation tunnels and this region has a lower permeability than that of the original formation matrix. The perforating operation also may generate perforation tunnels full of debris, e.g. rock debris mixed with perforator charge debris. The extent of the damage and the amount of loose debris in the tunnel is dictated by a variety of factors, such as formation properties, explosive charge properties, pressure conditions, fluid properties, and/or other factors. The shock damaged region and the loose debris in the perforation tunnels can impair the productivity of production wells or the injectivity of injector wells.